A constitutive model for gas hydrate-bearing sediments considering hydrate occurring habits

Not only hydrate amount but also occurrence habits of hydrate in sediments influence the mechanical characteristics of gas hydrate-bearing sediments (GHBS). In constitutive models proposed recently, however, the influence of occurrence habits is not considered. Based upon the influence mechanism of occurrence habits of hydrate on mechanical behaviors of GHBS, a novel concept, called effective saturation of hydrate, is proposed to address the influence of occurrence habit of hydrate. Referring to the statistical damage constitutive model for GHBS by previous researchers, a statistical damage constitutive model considering occurrence habits of hydrate is developed. In this model, the strengths of microelements for GHBS are assumed to obey the Weibull distribution, and the strength of microelement is calculated using the Drucker-Prager strength criterion. A modified empirical formula of elastic modulus is suggested to consider the effect of hydrate saturation and testing confining pressure. Meanwhile, the relationships between model parameters m and F-0, hydrate saturation s(h) and confining pressure sigma(3) are analyzed; then the fitting expressions are furtherly proposed. Finally, it is demonstrated that this model can simulate well the stress-strain curves of GHBS, and has capacity of reflecting the stiffness, strength and softening characteristics of GHBS.